1. Field of the Invention
The present invention relates to a powdery fuel combustion apparatus applicable to a thermal power generation boiler furnace, a chemical industry furnace and the like.
2. Description of the Prior Art
FIG. 7 is a horizontal cross sectional view showing one example of a prior art powdery fuel combustion apparatus. In FIG. 7, numeral 1 designates a burner nozzle, numeral 2 designates a burner nozzle opening plane, numeral 3 designates a powdery fuel supply pipe, numeral 4 designates a combustion assisting air supply passage, numeral 5 designates a wind box, numeral 6 designates a multiplicity of furnace wall tubes, numeral 7 designates a furnace side plane and numeral 11 designates an extension plane of the furnace side plane 7.
A mixed flow of a powdery fuel and a carrying air passes through the powdery fuel supply pipe 3 to be led to the burner nozzle 1 to be then jetted into a furnace from the burner nozzle opening plane 2. Combustion assisting air passes through the combustion assisting air supply passage 4 to be led to the burner nozzle 1 to be then jetted into the furnace from the burner nozzle opening plane 2, like the mixed flow of the powdery fuel and the carrying air. A jetting directional axis 8 is a central axis extending along the direction of the jetting of the fuel and air and a vertical plane passing through the jetting directional axis 8 does not intersect the furnace side plane 7 orthogonally but at an angle.
The jetted powdery fuel and carrying air as well as the combustion assisting air, while they are diffusing and mixing with one another, form flames. At this time, if there occurs such a phenomenon that the flames impinge on the furnace wall tubes 6 or lick on the furnace wall tubes 6, the flames will be cooled by the furnace wall tubes 6, which may result in a deterioration of combustibility due to an increase of combustibles in ash or in what is referred to as clinker trouble in which clinker sticks to the furnace wall tubes 6.
Thus, in the prior art, in order to prevent the flames from impinging on the furnace wall tubes 6, a portion of the furnace wall tubes 6 near the burner nozzle 1 is not arranged in the extension plane 11 of the furnace side plane 7 but is arranged in a row toward the wind box 5 side, as shown by a row 26 of the furnace wall tubes 6, in consideration of flame spreading, wherein an angle xcex1 is formed between the furnace side plane 7 and the row 26 of the furnace wall tubes 6.
A jetting directional axis along which the combustion assisting air is jetted into the furnace is coaxial with the jetting directional axis 8 along which the powdery fuel and the carrying air are jetted into the furnace. Also, a cross sectional shape of the burner nozzle 1 is a right and left plane symmetric shape, where a vertical plane passing through the jetting directional axis 8 is the symmetry plane.
FIG. 8 is what is called a burner panel structure conceptual view (plan view), wherein a conceptual view of the structure of the furnace wall tubes 6 arranged around the prior art powdery fuel combustion apparatus of FIG. 7 is shown. Each line element shown in FIG. 8 represents one of the furnace wall tubes 6.
In the prior art powdery fuel combustion apparatus mentioned above, in consideration of preventing increased combustibles in ash or preventing clinker trouble, the partial furnace wall tubes 6 near the burner nozzle 1 are arranged in the row 26 toward the wind box 5 side with the angle xcex1 between the furnace side plane 7 and the row 26 and this arrangement is considered sufficient performance-wise. However, there are still problems to be improved structurally, as follows:
(1) The row 26 portion of the furnace wall tubes 6 is not located in the same plane as the furnace side plane 7 or the extension plane 11 of the furnace side plane 7, hence the work of a furnace wall tube panel or a burner panel is not facilitated.
(2) A furnace wall support structure becomes complicated.
(3) In the case of a large capacity burner or a large capacity boiler, a length L of the row 26 of the furnace wall tubes 6 becomes large relative to a furnace width or a furnace depth, hence access to the surroundings of the furnace wall becomes difficult which inconveniences the maintenance of the furnace.
(4) The burner nozzle 1 is located on a comparatively outer side of the furnace, hence maintainability thereof is not high.
In order to solve the problems in the prior art, the inventors here disclose a powdery fuel combustion apparatus comprising a burner nozzle, disposed on a furnace side plane of a vertical square body type furnace, for jetting a mixed flow of a powdery fuel and air as well as a combustion assisting air therearound. A powdery fuel supply pipe, connected to said burner nozzle, is provided for supplying the powdery fuel and air. Also, a wind box is connected to the burner nozzle via the powdery fuel supply pipe and forms a combustion assisting air supply passage disposed around the powdery fuel supply pipe. The powdery fuel combustion apparatus is constructed such that a vertical plane passing through a jetting directional axis of the mixed flow does not cross the furnace side plane orthogonally. The burner nozzle has a right and left non-symmetric shape with respect to the vertical plane and has its tip portion opening plane located in a plane which is same as or parallel to the furnace side plane.
In the powdery fuel combustion apparatus of the present invention constructed as above, the burner nozzle has a right and left non-symmetric shape with respect to the vertical plane passing through the jetting directional axis of the mixed flow of the powdery fuel and air. The nozzle has its tip portion opening plane located in the plane which is same as or parallel to the furnace side plane, and thus the mixed flow of the powdery fuel and carrying air as well as the flow of the combustion assisting air, both jetted from the burner nozzle opening plane, can form flames in a more inner side place of the furnace than in a place at the furnace side plane and extension plane thereof or near these planes. Hence, such a phenomenon that the flames impinge on the furnace wall tubes or lick on the furnace wall tubes can be prevented and also the partial furnace wall tubes located near the burner nozzle are arranged on the furnace side plane, thereby the structural portions of the furnace and the like can be simplified.
Also, the present invention provides a powdery fuel combustion apparatus as mentioned above, wherein there are provided a swirler type disperser in a bent portion of the powdery fuel supply pipe or on a burner nozzle side of the bent portion as well as provided a rich/lean separator near the burner nozzle in the powdery fuel supply pipe.
That is, the powdery fuel, which has been carried by the carrying air in the powdery fuel supply pipe from the upstream side, is dispersed by the swirler type disperser located in the bent portion or on the burner nozzle side of the bent portion so that the distribution thereof becomes uniform and then the mixed flow of the powdery fuel and the air is separated into a fuel rich portion and a fuel lean portion by the rich/lean separator to be jetted into the furnace. Thereby the fuel separated into the rich/lean portions is supplied into the furnace so that a combustion in which NOx is reduced can be effected.
Further, the present invention provides a powdery fuel combustion apparatus as mentioned above, wherein the wind box constitutes a unit wind box comprising two powdery fuel supply pipes and five combustion assisting air supply passages. One of the supply passages is disposed between the two powdery fuel supply pipes and four being disposed so as to open in a double form, respectively, around each of the two powdery fuel supply pipes and there are provided a plurality of the unit wind boxes.
That is, according to the present invention, the unit wind box is constructed such that the powdery fuel supply pipe is separated into two parts and the combustion assisting air supply passage is separated into five parts and there are provided the plurality of the unit wind boxes. Thereby the supply of the powdery fuel and the combustion assisting air can be controlled finely and a timely control of the combustion becomes possible so that an optimum combustion state may be obtained.
Also, the present invention provides a powdery fuel combustion apparatus as mentioned above, wherein a jetting portion for jetting the combustion assisting air into the furnace is constructed by a burner throat in place of the burner nozzle.
That is, according to the present invention, out of the mixed flow of powdery fuel and air and the combustion assisting air which are to be supplied into the furnace, the combustion assisting air is supplied not through the burner nozzle but through the burner throat, thereby the construction of the jetting portion of the combustion assisting air which tends to become complicated can be further simplified.